Electrical conductor



OCe 13, 1942. R, W|LL|AM5 2,298,324

ELECTRICAL CONDUCTOR Filed Sept. 29, 1934 /NVENTUR RJ?. W/LL/AMS v ATTORNEY- Patented Oct. 13, 1942 ELECTRICAL CONDUCTOR Robert R. Williams, Roselle, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application September 29, 1934, Serial No. 746,026

12 Claims.

This invention relates to electrical conductors and more particularly to an'insulating covering for such conductors.

In the manufacture of electrical conductors, it is desirable to insulate the conductor with a material which is porous or fibrous in order to reduce the capacitance of the circuit and, in addition, it is very important that the electrical characteristics ofthe insulation be substantially free from variations due to changes in humidity. In Wire to be used in high. frequency work, it is also desirable to employ an insulation which has constancy of electrical properties over a wide range of frequencies.

An object, therefore, of the present invention is a conductor insulated with a dielectric material having the above mentioned desirable characteristics.

Another object is to secure mechanical separation of circuits by a layer of insulation which is composed of air as largely as possible combined with solid materials of superior, inherent electrical characteristics.

In accordance wit-h one feature of the present invention, these and other objects are attained by insulating the conductor with one or more substantially pure hydrocarbon compounds. This material may be extruded upon the conductor or it may be drawn into filaments and loosely wound upon the conductor. may be coated with a layer of the hydrocarbon material and a filament layer wound thereover.

In accordance with another feature of the invention, the hydrocarbon insulation is made p0- rous by subjecting the material or the conductor coated with the material to a vacuum treatment at an elevated temperature whereby the hydrocarbon material puffs up into a very porous mass having a low dielectric capacity.

A clearer understanding of this invention may be had by reference to the accompanying drawing in which:

Fig. 1 is a view of a conductor insulated in accordance with the invention with an extruded hydrocarbon compound which is, in turn, covered by an impregnated textile serving;

Fig. 2 is a view of a conductor insulated with filaments of the iwdrocarbon compound;

Fig. 3 is a view of a conductor insulated with a layer of the extruded compound over which is placed a winding of hydrocarbon filament; and

Fig. 4 is a view of a, conductor insulated with a vacuum-treated 4hydrocarbon material.

Referring to Fig. 1, there is shown a conduct- If desired, the conductor ing core Il) insulated by a layer of a hydrocarbon 55 II, preferably of high molecular weight, such as polymerized vinyl benzene hydrocarbon, which is also known as polystyrol and meta-styrene. Other substantially purev hydrocarbons may be used under certain conditions such as, for example, balata or gutta percha hydrocarbon.

Polymerized vinyl benzene or polymerized vinyl benzene resin, as it is sometimes called, is .characterized by extremely high insulation resistance, low dielectric constant, low conduction, low power factor, low surface leakage and retention of good dielectric properties at high humidity. It is, therefore, particularly applicable to insulating electrical apparatus.

For some uses, Wire insulated only with meta styrene will be satisfactory but if it is so desired, a textile serving I2 may be placed over the insulation layer for the purpose of protecting the insulation layer and for increasing its physical strength. This textile serving may be impregnated with any of the well-known impregnating materials shown at I3, such as waxes, drying oil compositions, phenolic condensation products, cellulose derivatives, and the like.

The meta styrene layer may also be covered directly with a suitable lacquer or a coating of plastic material and the wires used in this form or covered with a textile serving.

Referring to Fig. 2, there is shown a conducting core l0 insulated with a winding I4 of filaments of meta styrene. These filaments may be wound around the wire singularly or in multiple ply. In general, it is desirable to insulate the Wire with more than one layer of filaments as shown at I5.

These filaments are Wound loosely around the conductor so as to permit airspaces to exist between the turns of the filament. Air is, of course, a superior dielectric material and in using this type of hydrocarbon filament insulation there is obtained mechanical separation of conductors by a surrounding of insulation which is largely composed of air and whose solid portion comprises a material having the superior electrical characteristics herein enumerated.

A satisfactory method of forming these filaments of hydrocarbon material is to heat the ma terial in a suitable receptacle and draw filaments out of the receptacle through one or more small orifices having diameters approximately that of the final product. The filament is then passed through a heating unit preferably having a gradual decrease in temperature and is then cooled in air before it is wound on a spool. The compound may be forced out of the orifice by gas pressure preferably by an inert gas. It has been found that by controlling the temperature and length of the heating unit that the diameter of the lament may be further regulated. Filament size is A dependent upon adjustment of several variables, namely, speed of drawing, temperature of the bath, temperature of the heating unit, andthe gas pressure. The resulting filament may be wound around the conductor in its present form or several small .laments may be twisted together into a yarn and this yarn wound upon the conductor.

In accordance with another method of forming laments of hydrocarbon compound, a plurality of laments may be formed and served directly around a conductor in one continuous operation.

Another method of insulating a conducting core with a hydrocarbon compound, as shown in Fig. 3, is to extrude the meta styrene compound Il on the conductor l and then wind filaments I4 of meta styrene loosely therearound.

Another method of insulating a conductor with a hydrocarbon compound having a large number of air spaces therein is shown in Fig. 4 in which a conductor l0 is shown insulated with a vacuumtreated hydrocarbon I6.

When a hydrocarbon compound, such as meta styrene, is placed in a vacuum and heated to about 100 C., it puffs up or explodes into a very porous mass. v

The mechanism of the puiiing process is believed to be as follows: Traces of solvent which, under ordinary conditions, are usually present in the solid hydrocarbon are vaporized by the heat andrvacuum treatment and the vapor pressure thus produced inside of the material blows it up, leaving numerous air spaces in the material. Ordinarily, the rate of diffusion of gas from materials is high enough to permit the gas to escape Without changing the dimensions of the solid, but, in this case expansion of the gas causes the solid to ilow and increase in volume.

The temperature at which this process is conducted can be varied over a wide range by varying theamount and the vapor pressure of the solvent left in the material.

Two methods can be used in applying this insulation to cables: The conductor can be coated with a coating of the hydrocarbon by passing it through a solution of the hydrocarbon in benzene or other suitable solventsand the film on the conductor can then be puffed up While the conductor is held in position, or, a thin layer of meta styrene suitably treated can be extruded on the conductor and this lm puied up as here described.

Il desired, the insulated conductors shown in Figs. 2, 3 and 4 also may be covered with an impregnated textile serving such as is shown in Fig. 1.

A comparison of wire insulated with filaments of meta styrene, with wire insulated with Washed silk, cellulose acetate silk and partially acetylated cotton at humidities ranging from 0 per cent to 96.6 per cent, shows that the Wire insulated with meta styrene is decidedly superior from the standpoint of low conductance, low capacitance, and 'low power factor at frequencies from 1 to 100 kilocycles. The experiments which were conducted also disclosed the superiority of meta styrene over other materials at high humidities and frequencies.

What is claimed is:

l. In an electrical conductor, a conducting core and an insulating covering therefor consisting of a plurality of layers of polymerized vinyl benzene in filament form.

2. In an electrical conductor, a conducting core and an insulating coatingtherefor consisting of a plurality of layers of a substantially pure polymerized vinyl benzene-hydrocarbon in lament form. f

3. In an electrical conductor, a conducting core and an insulating covering thereon, said covering comprising an inner coating of meta styrene and a serving of meta styrene in lament form thereover.

4.V In an electrical conductor, a conducting core, and an insulating covering therefor, comprising a plurality of layers of meta styrene and one of said layers being in lament form.

5. A cable for communication purposes, comprising a flexible insulating sleeve, a iiexible electric conductor enclosed in said sleeve, the latter consisting of a pure polymerization product of a substituted benzene, in which each substitute radical comprises a vinyl group, said polymerization product being an unplasticized, synthetic, organic product which is homogeneous, isotropic,

and substantially non-hygroscopic, and free .from

9. A cable'for transmission of intelligence and l other purposes, comprising an insulating sleeve and an electric conductor disposed inside said sleeve, the latter consisting of an unplasticized layer of Polystyrol of suflicient thinness to assure iiexibility.

10. In an electrical conductor, a conducting core and an insulating covering thereon comprising laments "consisting of polymerized vinyl ben-4 Zelle.

11. In an electrical conductor, a conducting core and an insulating covering thereon, said covering comprising an inner coating consisting of polymerized vinyl benzene and an outer covering com- 

